But just how much will Liverpool miss him, and where do they need to invest the £142m fee?

With the help of former Reds defender Mark Lawrenson and chief football writer Phil McNulty, BBC Sport attempts to answer these questions and more besides, while Spanish football writer Andy West considers just where Coutinho will fit into the current Barcelona squad.

A big loss for Liverpool?

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There is no doubt that Coutinho has been a massive player for Liverpool since arriving in January 2013.

He has scored 54 goals in over 200 appearances, hitting double figures in each of the last three seasons.

The Brazilian was the club’s joint top scorer in the Premier League last term with 13 goals and was well on course to surpass that total in the current campaign, leaving Anfield with seven goals.

But what Liverpool will miss more than his goals is his ability to create chances for his team-mates and make those around him better.

In terms of goals, no player has scored more than Roberto Firmino since he joined the club in the summer of 2015 (30 goals) but without Coutinho alongside him, the Brazilian forward is not as effective.

Firmino has scored six goals in the 11 games they have started together this season, but in the seven games he has started without his compatriot, the 26-year-old has managed just three.

Indeed, not even former Liverpool defender Jamie Carragher, who played alongside Coutinho in the early part of the Brazilian’s career at Anfield, could have envisaged such a rise.

Carragher tweeted: “Disappointed Coutinho has gone, never thought he’d turn into the player he’s become when I first played with him, but he’s been a great Liverpool player these last few years.”

But Salah is softening the blow, right?

Mohamed Salah’s sensational form this season has no doubt provided a welcome distraction to the Coutinho saga for Liverpool fans.

The Egypt international has scored 17 goals in 21 Premier League games since joining in the summer, and his stats certainly stack up well against Coutinho.

Salah has scored 10 more goals than Coutinho so far in 2017-18, although the latter provided more assists (six to Salah’s five) and created more chances overall (40 to 35) in fewer games (14 to 21).

But in terms of first-season influence, Salah is having a bigger impact on Liverpool than Coutinho did, as the below table highlights.

First 21 Liverpool Premier League games

Coutinho

Salah

21

Games played

21

1493

Minutes played

1596

4

Goals

17

5

Assists

5

61

Shots (including blocked shots)

82

31

Chances created (including assists)

35

35

Dribbles completed

52

How do Liverpool replace Coutinho?

BBC Sport’s chief football writer Phil McNulty:

The departure of such a key figure as Coutinho is, of course, a blow to Liverpool.

He has developed into an outstanding player, a maturity illustrated by the increase in his value to £142m after costing Liverpool just £8.5m from Inter Milan in January 2013.

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It is a setback that is cushioned by the stunning impact made by summer signing Salah, not strictly a player in the Coutinho mould but a creator and goalscorer more than capable of carrying a major burden as Liverpool chase a top-four place, the Champions League and the FA Cup.

Salah has illuminated Liverpool with his pace, strength and his astonishing goalscoring, a world away from the younger version who failed to make an impact at Chelsea.

Liverpool’s so-called ‘Fab Four’ broke up quickly but Salah, Sadio Mane and Firmino have shown enough to suggest that Coutinho’s departure, while it cannot be dismissed, can be covered.

Liverpool with and without Coutinho in 2017-18

With Coutinho starting

Premier League

Without Coutinho starting

Liverpool have picked up more points per game without Coutinho this season than with him

13

Games

9

6

Wins

6

6

Draws

2

1

Losses

1

46.20

Win %

66.70

1.8

Points per game

2.2

Midfield enforcement of a different sort will arrive when Naby Keita joins from RB Leipzig in the summer, so manager Jurgen Klopp will have been exploring various options.

And what about Alex Oxlade-Chamberlain? He was brought to Anfield on the promise of a central midfield role – maybe he will be given a lengthy period to impress.

How must Liverpool spend the money?

It is naive in the extreme to suggest Klopp and those behind the scenes at Anfield have not been looking at succession planning to compensate for the loss of Coutinho – but equally, do not expect a spending spree within hours of the money clearing.

Liverpool may have an initial £105m in the bank from the sale, but it will not burn a hole in Klopp’s pocket and he will only spend on who he wants, although the £75m spent on Virgil van Dijk shows he will also spend what it takes.

Klopp continues to be linked with Monaco’s Thomas Lemar but it is likely the list of potential replacements and those who could be brought in with the Coutinho money has already been drawn up.

Liverpool’s recent spending under Klopp may have brought some expensive purchases but it has been a measured and carefully structured approach.

And as the long game that led to the signing of Van Dijk proved, Klopp has firm ideas on who he wants and rarely likes to venture into Plan B territory.

‘There’s a fella at Arsenal who wants out…’

Leicester forward Riyad Mahrez has been linked, but former Liverpool player Lawrenson believes Alexis Sanchez would be the ideal replacement for Coutinho.

Sanchez’s future at Arsenal appears increasingly uncertain, with Manchester City – who failed in their attempt to sign the Chile international last summer – likely to move again for the forward this month,

“There is a fella at Arsenal who wants out called Alexis Sanchez, that would be very interesting if Liverpool decide to go for someone like that,” says Lawrenson.

“If you can get Sanchez, and you have already got Virgil van Dijk, then that is good business, probably good business for everyone.”

As big a blow as Suarez’s departure?

Liverpool with and without Coutinho since 13-02-2013

With Coutinho starting

Premier League

Without Coutinho starting

137

Games

50

75

Wins

26

35

Draws

13

27

Losses

11

54.70

Win %

52

1.9

Points per game

1.8

The departure of such an influential player stirs memories of Fernando Torres’ £50m move to Chelsea in 2011 and Barcelona’s signing of Luis Suarez in 2014.

But can Coutinho’s departure be compared to those? And is the club’s reaction to previous big-name departures a reason for optimism for Liverpool fans?

“[Torres and Suarez] were both very, very good for Liverpool,” says Lawrenson, “but when you think of it like that it does soften the blow for it because it is a case of, ‘the King is dead, long live the King’.

“The loss of Coutinho is a blow but I don’t think it is insurmountable. It is not like Tottenham losing Harry Kane, is it?”

Where will Coutinho fit in at Barcelona?

Spanish football writer Andy West:

Barcelona have never made a secret of the fact that Coutinho is their number one target to provide more creative flair to their midfield, with the Brazilian earmarked as the long-term replacement for club captain Andres Iniesta, who will be 34 by the end of the season.

And the importance of Iniesta explains why Barca have been so determined to complete the deal now, rather than waiting until the summer.

With La Liga effectively already won, the Catalan club are now turning their main focus onto regaining the Champions League crown, and Iniesta will be vital to that quest.

Even Lionel Messi can’t do everything by himself, and the presence of a fit and healthy Iniesta will make a major difference in giving Barca the best possible chance of breaking down the continent’s best defences.

The arrival of Coutinho, therefore, means that Iniesta can be safely rested for league games without the team suffering a significant drop-off in quality, allowing the ageing skipper to reserve his energies for the European stage.

Tactically, Coutinho’s biggest challenge will be learning how to combine effectively with Messi and help create space for the Argentine – around whom everything revolves – rather than getting in his way.